Polishing composition and polishing method employing it

ABSTRACT

A polishing composition comprising:  
     (a) an abrasive,  
     (b) a compound to form a chelate with copper ions  
     (c) a compound to provide a protective layer-forming function to a copper layer,  
     (d) hydrogen peroxide, and  
     (e) water,  
     wherein the abrasive of component (a) has a primary particle size within a range of from 50 to 120 nm.

[0001] The present invention relates to a polishing composition to beused for polishing substrates for semiconductors, photomasks and variousmemory hard disks, particularly to a polishing composition useful forpolishing for planarization of the surface of device wafers in e.g.semiconductor industry, and a polishing method employing such acomposition.

[0002] More particularly, the present invention relates to a polishingcomposition which is highly efficient and useful for forming anexcellent polished surface in the polishing step of semiconductordevices to which so-called chemical mechanical polishing technology isapplied, in the processing of device wafers, and a polishing methodemploying such a composition.

[0003] Progress of so-called high technology products includingcomputers has been remarkable in recent years, and parts to be used forsuch products, e.g. devices such as ULSI, have been developed for highintegration and high speed, year after year. Along with such progress,the design rule for semiconductor devices has been progressively refinedyear after year, the depth of focus in a process for producing devicestends to be shallow, and planarization required for the pattern-formingsurface tends to be increasingly severe.

[0004] Further, to cope with an increase in resistance of the wiring dueto refinement of the wiring, it has been studied to employ copperinstead of tungsten or aluminum, as the wiring material.

[0005] By its nature, copper is highly susceptible to etching, andaccordingly, it requires the following process. Namely, after formingwiring grooves and vias on an insulating layer, copper wirings areformed by sputtering or plating, and then an unnecessary copper layerdeposited on the insulating layer is removed by chemical mechanicalpolishing (hereinafter referred to as CMP) which is a combination ofmechanical polishing and chemical polishing.

[0006] However, in such a process, it may happen that copper atoms willdiffuse into the insulating layer to deteriorate the device properties.Therefore, for the purpose of preventing diffusion of copper atoms, ithas been studied to provide a barrier layer on the insulating layerhaving wiring grooves or vias formed. As a material for such a barrierlayer, tantalum metal, tantalum nitride or a tantalum compound(hereinafter will generally be referred to as a tantalum-containingcompound) is most suitable also from the viewpoint of the reliability ofthe device and is expected to be employed mostly in the future.

[0007] Accordingly, in such a CMP process for a semiconductor devicecontaining such a copper layer and a tantalum-containing compound,firstly the copper layer as the outermost layer and then thetantalum-containing compound layer as the barrier layer, are polished,respectively, and polishing will be completed when it has reached theinsulating layer of e.g. silicon dioxide or monofluoro silicon oxide(SiOF). As an ideal process, it is desired that by using only one typeof a polishing composition, the copper layer and the tantalum-containingcompound layer are uniformly removed by polishing in a single polishingstep, and polishing will be completed certainly when it has reached theinsulating layer. However, copper and a tantalum-containing compound aredifferent in their hardness, chemical stability and other mechanicalproperties and accordingly in the processability, and thus, it isdifficult to adopt such an ideal polishing process. Accordingly, thefollowing two step polishing process, i.e. a polishing process dividedinto two steps, is being studied.

[0008] Firstly, in the first step polishing (hereinafter referred to asthe first polishing), using a polishing composition capable of polishinga copper layer at a high efficiency, the copper layer is polished usinge.g. a tantalum-containing compound layer as a stopper until such atantalum-containing compound layer is reached. Here, for the purpose ofnot forming various surface defects such as recesses, erosion, dishing,etc., on the copper layer surface, polishing may be terminatedimmediately before reaching the tantalum-containing compound layer i.e.while a copper layer still slightly remains. Then, in the second steppolishing (hereinafter referred to as the second polishing), using apolishing composition capable of polishing mainly a tantalum-containingcompound layer at a high efficiency, the remaining thin copper layer andthe tantalum-containing compound layer are continuously polished usingthe insulating layer as a stopper, and polishing is completed when ithas reached the insulating layer.

[0009] The polishing composition to be used in the first polishing isrequired to have a property such that it is capable of polishing thecopper layer at a high stock removal rate without forming theabove-mentioned various surface defects (such as recesses) on the copperlayer surface, which can not be removed by the second polishing.

[0010] With respect to such a polishing composition for polishing acopper layer, for example, JP-A-7-233485 (Prior Art 1) discloses apolishing liquid for a copper type metal layer, which comprises at leastone organic acid selected from the group consisting of aminoacetic acid(hereinafter referred to as glycine) and amidesulfuric acid, anoxidizing agent and water, and a method for producing a semiconductordevice using such a polishing liquid. If this polishing liquid is usedfor polishing a copper layer, a relatively high stock removal rate isobtainable. It is believed that copper atoms on the copper layer surfaceare converted to copper ions by the action of the oxidizing agent, andthe copper ions are taken into a chelate compound, whereby a high stockremoval rate can be obtained.

[0011] However, as a result of experiments conducted by the presentinventors, it has been found that when a polishing liquid merelycontaining an abrasive, glycine and hydrogen peroxide, like thepolishing liquid of the above-mentioned Prior Art 1, is used forpolishing a copper layer having a pattern formed, many pits (dents) willform in the copper wiring. This phenomenon is frequently observedparticularly at a fine wiring of 0.3 μm or less. This may be explainedsuch that defects or impurities are present during formation of thecopper layer at the fine wiring, and such weak layer portions areattacked by a chemical or mechanical action during the polishing,whereby pits will be formed. Accordingly, it is desired to furtherimprove the uniformity of the layer formation by optimizing thelayer-forming conditions in the preparation of semiconductor devices. Onthe other hand, it is strongly desired to develop a polishingcomposition which does not form pits during the polishing.

[0012] The present invention has been made to solve such a problem, andit is an object of the present invention to provide a polishingcomposition which is capable of preventing formation of pits in thecopper wiring in a CMP process in the production of a semiconductordevice comprising at least a copper layer and a tantalum-containingcompound layer, and a polishing method employing it.

[0013] The present invention provides a polishing compositioncomprising:

[0014] (a) an abrasive,

[0015] (b) a compound to form a chelate with copper ions

[0016] (c) a compound to provide a protective layer-forming function toa copper layer,

[0017] (d) hydrogen peroxide, and

[0018] (e) water,

[0019] wherein the abrasive of component (a) has a primary particle sizewithin a range of from 50 to 120 nm.

[0020] The present invention provides the polishing composition, whereinthe abrasive of component (a) is silicon dioxide.

[0021] The present invention provides the polishing composition, whereinthe abrasive of component (a) is fumed silica or colloidal silica.

[0022] The present invention provides the polishing composition, whereinthe content of the abrasive of component (a) is within a range of from 5to 50 g/l based on the composition.

[0023] The present invention provides the polishing composition, whereinthe compound to form a chelate with copper ions of component (b), is atleast one member selected from the group consisting of glycine,α-alanine, serine, quinaldic acid, hystidine and derivatives thereof,and its content is within a range of from 5 to 50 g/l based on thecomposition.

[0024] The present invention provides the polishing composition, whereinthe compound to provide a protective-layer forming function to a copperlayer, of component (c), is at least one member selected from the groupconsisting of benzotriazole and derivatives thereof, and its content iswithin a range of 0.0002 to 0.002 mol/l based on the composition.

[0025] The present invention provides the polishing composition, whereinthe content of the hydrogen peroxide of component (d) is within a rangeof from 0.03 to 1 mol/l based on the composition.

[0026] The present invention provides a polishing method which comprisespolishing a semiconductor device having at least a layer of copper and alayer of a tantalum-containing compound formed on a substrate, with thepolishing composition.

[0027] Now, the present invention will be described in further detail.However, it should be understood that the following description isintended to facilitate the understanding of the present invention, andby no means restrict the present invention.

[0028] Abrasive

[0029] The abrasive as one component of the polishing composition of thepresent invention serves to perform mechanical polishing in the CMPprocessing and has a function to mechanically remove a brittle layerformed on the surface to be polished. As such an abrasive, it iscommonly known to use silicon dioxide, aluminum oxide, cerium oxide,titanium oxide, zirconium oxide, silicon carbide, silicon nitride, etc.Among these abrasives, one or more may be used. In the presentinvention, it is preferred to use silicon dioxide. Further, fumed silicaand colloidal silica or either one of them, may be used, and colloidalsilica is most preferred.

[0030] Further, the abrasive has a primary particle size within a rangeof from 50 to 120 nm, preferably from 70 to 100 nm. The most importantpoint in the present invention is that when the primary particle size ofthe abrasive is within the above range, such is effective forsuppressing pits on the copper wiring. The primary particle size of from50 to 120 nm is a particle size which means an intermediate between acolloidal state and a non-colloidal state. According to an observationby the present inventors, in a completely colloidal state, i.e. when theprimary particle size of the abrasive is smaller than 50 nm, the surfaceof the abrasive will be in a very active state, and such an activesurface is believed to induce pits on the copper wiring. As the primaryparticle size increases, the colloidal nature decreases, and theactivity of the particle surface tends to be small. Consequently, pitstend to hardly develop. On the other hand, if the primary particle sizeis too large, i.e. when the primary particle size of the abrasiveexceeds 120 nm, the dispersibility of the abrasive tends to be poor, andconsequently, scratching is likely to be led, and handling at the timeof supplying the slurry tends to be difficult.

[0031] The primary particle size of the abrasive according to thepresent invention is a primary particle size calculated from a value ofa specific surface area measured by a nitrogen adsorption method (BETmethod). To obtain a primary particle size from the value of a specificsurface area measured by the BET method, such a primary particle size iscalculated by the mathematical formula (A).

D=6/ρ·S  (A)

[0032] wherein D is the primary particle size (nm), ρ is the specificgravity (g/cm³) of the abrasive, and S is the specific surface area(m²/g) measured by the BET method.

[0033] Further, the content of the abrasive in the polishing compositionis usually from 5 to 50 g/l, preferably from 10 to 30 g/l, morepreferably from 15 to 25 g/l. If the content of the abrasive is toosmall, the mechanical polishing power decreases, whereby the stockremoval rate of the copper layer is likely to decrease. On the otherhand, if the content of the abrasive is too large, the mechanicalpolishing power increases, and the rate of polishing thetantalum-containing compound layer tends to be too high and difficult tocontrol.

[0034] Compound to Form a Chelate with Copper Ions

[0035] The compound to form a chelate with copper ions, as one componentof the polishing composition of the present invention, is characterizedin that it contains at least one carboxyl group and a nitrogen atom,which are located at the α-position. The carboxyl group and the nitrogenatom located at the α-position will form a chelate with copper, andthereby accelerate polishing of the copper layer. In the presentinvention, it is at least one member selected from the group consistingof glycine, α-alanine, serine, quinaldic acid, hystidine and derivativesthereof.

[0036] The content of the compound to form a chelate with copper ions,in the polishing composition, is usually from 0.04 to 0.2 mol/l,preferably from 0.06 to 0.12 mol/l, based on the composition. If thecontent is less than 0.04 mol/l, the stock removal rate of the copperlayer tends to be low, such being undesirable. On the other hand, if itexceeds 0.2 mol/l, the stock removal rate of the copper layer tends tobe too high and difficult to control, such being undesirable.

[0037] Compound to Provide a Protective Layer-forming Function to aCopper Layer

[0038] The compound to provide a protective layer-forming function to acopper layer, as one component of the polishing composition of thepresent invention, has a role to protect the copper layer during and/orafter the polishing, and consequently, it suppresses dishing orformation of recesses in the copper wiring and has a function as acorrosion-preventing agent to suppress corrosion of the copper. Such acompound to provide a protective-layer forming function to a copperlayer, is at least one member selected from the group consisting ofbenzotriazole and its derivatives. The derivatives may, for example, bebenzoimidazole, triazole, imidazole and tolyltriazole.

[0039] The content of the compound to provide a protective layer-formingfunction to a copper layer, in the polishing composition, is usuallyfrom 0.0002 to 0.002 mol/l, preferably from 0.0003 to 0.001 mol/l, basedon the composition. If the content is less than 0.0002 mol/l, thesurface of the copper layer after polishing tends to be susceptible tocorrosion, such being undesirable. On the other hand, if it exceeds0.002 mol/l, the protective layer-forming function to the copper tendsto be strong, whereby non-uniformity in polishing is likely to be led,or the stock removal rate of the copper layer tends to be excessivelylow, such being undesirable.

[0040] Hydrogen Peroxide

[0041] Hydrogen peroxide as one component of the polishing compositionof the present invention, is one functioning as an oxidizing agent. And,hydrogen peroxide has a characteristic such that one having a sufficientoxidizing power to oxidize the copper layer and containing no metal ionas an impurity, can readily be available, and thus, it is particularlysuitable for the polishing composition of the present invention.

[0042] The content of hydrogen peroxide in the polishing composition isusually from 0.03 to 1 mol/l, preferably from 0.1 to 0.5 mol/l, based onthe composition. If the content of hydrogen peroxide is too small, ortoo large, the stock removal rate of the copper layer tends to decrease.

[0043] Water

[0044] Water as one component of the polishing composition of thepresent invention is preferably one having impurities reduced as far aspossible, so that the above-mentioned respective components canprecisely perform their roles. Namely, water is preferably distilledwater, or one having impurity ions removed by an ion exchange resin andhaving suspended matters removed by a filter.

[0045] Polishing Composition

[0046] The polishing composition of the present invention is prepared bymixing, dissolving or dispersing the above-described respectivecomponents, i.e. the abrasive having a primary particle size within arange of from 50 to 120 nm, the compound to form a chelate with copperions, the compound to provide a protective layer-forming function to acopper layer and hydrogen-peroxide, in water. Here, a method for mixing,dissolving or dispersing is optional. For example, stirring by avane-type stirrer or ultrasonic dispersion may be employed. By such amethod, soluble components will be dissolved and insoluble componentswill be dispersed, whereby the composition will be a uniform dispersion.

[0047] Further, at the time of preparing the above polishingcomposition, a pH-adjusting agent to adjust the pH, various surfactantsand other additives may be incorporated as the case requires, for thepurpose of securing the safety or maintenance of the quality of theproduct, or depending upon the type of the object to be polished, thepolishing conditions and other requirements for polishing operation.

[0048] The pH-adjusting agent is used to improve the stability of thepolishing composition, to improve the safety in use or to meet therequirements of various regulations. As a pH-adjusting agent to be usedto lower the pH of the polishing composition of the present invention,hydrochloric acid, nitric acid, sulfuric acid, chloroacetic acid,tartaric acid, succinic acid, citric acid, malic acid, malonic acid,various fatty acids, various polycarboxylic acids, etc., may beemployed. On the other hand, a pH-adjusting agent to be used for thepurpose of raising the pH, potassium hydroxide, sodium hydroxide,ammonia, ethylenediamine, piperazine, polyethyleneimine, etc., may beemployed. The polishing composition of the present invention is notparticularly limited with respect to the pH, but it is usually adjustedto pH 3 to 10.

[0049] The surfactant is used to increase the dispersibility of theabrasive or to adjust the viscosity or the surface tension of thepolishing composition. The surfactants which may be used in the presentinvention, include, for example, a dispersing agent, a wetting agent, athickener, a defoaming agent, a foaming agent, a water repellent, etc.The surfactant to be used as a dispersing agent, may usually be asulfonate, phosphate, carboxylate or nonionic surfactant.

[0050] For the preparation of the polishing composition of the presentinvention, there is no particular restriction as to the order of mixingthe various additives or the mixing method.

[0051] The polishing composition of the present invention may beprepared, stored or transported in the form of a stock solution having arelatively high concentration, so that it may be diluted for use at thetime of actual polishing operation. The above-mentioned range for theconcentration is one for the actual polishing operation. Needless tosay, in the case of adopting such a method of diluting at the time ofactual use, the stock solution during the storage or transportation is asolution having a higher concentration. From the viewpoint of handlingefficiency, it is preferred to prepare the composition in such a highlyconcentrated form.

[0052] Further, hydrogen peroxide has a characteristic such that itdecomposes in the presence of metal ions, ammonium ions or an amine.Accordingly, it is advisable to add and mix it to the polishingcomposition immediately prior to the actual use for polishing operation.Such decomposition of hydrogen peroxide can be suppressed byincorporating a carboxylic acid or an alcohol. Namely, it is possible toobtain such an effect by the above-mentioned pH-adjusting agent.However, such decomposition will be influenced also by the storageenvironment, and there is a possibility that part of hydrogen peroxideundergoes decomposition due to a temperature change duringtransportation or due to formation of a stress. Accordingly, it ispreferred to carry out the mixing of hydrogen peroxide immediatelybefore polishing.

[0053] Polishing Method

[0054] The polishing method of the present invention comprises polishinga semiconductor device having at least a layer of copper and a layer ofa tantalum-containing compound formed on a substrate, with a polishingcomposition comprising the above-described respective components i.e. anabrasive having a primary particle size within a range of from 50 to 120nm, a compound to form a chelate with copper ions, a compound to providea protective layer-forming function to a copper layer, hydrogen peroxideand water.

[0055] This polishing method provides a high stock removal rate of thecopper layer and a low stock removal rate of the tantalum-containingcompound layer, whereby it provides a high selectivity ratio (the ratioof the stock removal rate of the copper layer to the stock removal rateof the tantalum-containing compound layer is referred to as a“selectivity ratio”), and the polished surface has excellent smoothness.Further, by specifying the primary particle size of the abrasivestrictly, it is possible to obtain a normal polished surface withoutformation of pits on the copper wiring on the substrate.

[0056] Such a polishing mechanism may be explained as follows. Firstly,by the action of hydrogen peroxide, the copper layer surface will beoxidized. Then, the compound to form a chelate with copper ions willdissolve in the polishing composition in the form of a copper chelate bya combined action with the abrasive. Further, for suppression of pits onthe copper wiring on the substrate, by specifying the particle size ofthe abrasive to be a relatively large particle size in a non-colloidalstate, the surface activity of the abrasive will be lowered, and anexcessive chemical reaction to the copper layer surface will besuppressed. It is believed that by these actions, it is possible torealize the high stock removal rate of the copper layer without formingpits on the copper wiring.

[0057] Now, the practical embodiments of the present invention will bedescribed in detail with reference to Examples. However, it should beunderstood that the present invention is by no means restricted to suchspecific Examples.

EXAMPLES 1 to 9 and COMPARATIVE EXAMPLES 1 to 6

[0058] Contents and Preparation of Polishing Compositions

[0059] Colloidal silica having various primary particle sizes as shownin Table 1, as an abrasive, glycine, hystidine or α-alanine, as acompound to form a chelate with copper ions (additive (b)),benzotriazole (hereinafter referred to as “BTA”) as a compound toprovide a protective layer-forming function to a copper layer (additive(c)), and hydrogen peroxide, were mixed with water so that they will beblended in such ratios as shown in Table 1, to obtain polishingcompositions of Examples 1 to 9 and Comparative Examples 1 to 6. Here,in Examples 1 to 9, the primary particle sizes of the abrasives werewithin a range of from 50 to 120 nm, and in Comparative Examples 1 to 6,the primary particle sizes of the abrasives were outside the aboverange. Further, as hydrogen peroxide, a commercially available 31%aqueous solution was employed, and it was mixed immediately prior topolishing. TABLE 1 Hydrogen Evaluation Abrasive Additive (b) Additive(c) peroxide of Particle Amount Amount Amount Amount polished size (nm)(g/l) Type (mol/l) Type mol/l) (mol/l) surface Ex. 1 50 20 Glycine 0.09BTA 0.0005 0.3 ◯ Ex. 2 70 20 Glycine 0.09 BTA 0.0005 0.3 ⊚ Ex. 3 90 20Glycine 0.09 BTA 0.0005 0.3 ⊚ Ex. 4 100 20 Glycine 0.09 BTA 0.0005 0.3 ⊚Ex. 5 120 20 glycine 0.09 BTA 0.0005 0.3 ◯ Ex. 6 70 20 Hystidine 0.12BTA 0.0005 0.3 ⊚ Ex. 7 90 20 Hystidine 0.12 BTA 0.0005 0.3 ⊚ Ex. 8 70 20α-alanine 0.15 BTA 0.0005 0.3 ⊚ Ex. 9 90 20 α-alanine 0.15 BTA 0.00050.3 ⊚ Comp. 30 20 Glycine 0.09 BTA 0.0005 0.3 P Ex. 1 Comp. 150 20Glycine 0.09 BTA 0.0005 0.3 S Ex. 2 Comp. 30 20 Hystidine 0.12 BTA0.0005 0.3 P Ex. 3 Comp. 150 20 Hystidine 0.12 BTA 0.0005 0.3 S Ex. 4Comp. 30 20 α-alanine 0.15 BTA 0.0005 0.3 P Ex. 5 Comp. 150 20 α-alanine0.15 BTA 0.0005 0.3 S Ex. 6

[0060] Polishing Tests

[0061] Using each of the polishing compositions of Examples 1 to 9 andComparative Examples 1 to 6, polishing of a layer-formed side of anobject to be polished, was carried out under the following conditions.

[0062] Object to be polished:

[0063] A patterned wafer having a copper wiring with a minimum wirewidth of 0.2 μum formed by electroplating

[0064] Polishing machine:

[0065] One side CMP polishing machine (AVANTI472, manufactured bySpeedfam-Ipec Co.)

[0066] Polishing pad:

[0067] Laminated polishing pad made of polyurethane (IC-1000/Suba400,manufactured by Rodel Inc., U.S.A.)

[0068] Polishing pressure: 4 psi

[0069] Table rotational speed: 50 rpm

[0070] Feed rate of the polishing composition: 250 cc/min

[0071] Rotational speed of the carrier: 50 rpm

[0072] For the end point of polishing, the end point was detected fromthe torque current of the carrier, and then, overpolishing correspondingto 10% in terms of time, was carried out, whereupon the polishing wasterminated.

[0073] After the polishing, the wafer was sequentially washed and dried,and the copper wiring of 0.2 μm was observed by an optical microscope,whereby evaluation of the polished surface condition after the polishingwas carried out in accordance with the following standards. The obtainedresults are shown in Table 1.

[0074] ⊚: Excellent with no substantial formation of pits.

[0075] ∘: A small number of small and shallow pits are observed, butwithin an allowable range.

[0076] P: Pits are observed.

[0077] S: Scratches are observed.

[0078] As is evident from Table 1, in Comparative Example 1, 3, or 5wherein the primary particle size of the abrasive is outside the rangeof from 50 to 120 nm i.e. smaller than 50 nm, the surface of theabrasive is in a very active state, whereby pits formed on the polishedsurface, and in Comparative Example 2, 4 or 6 wherein the primaryparticle size of the abrasive is larger than 120 nm, the dispersibilityof the abrasive is poor, and scratches were formed on the polishedsurface, and in either case, polishing with high efficiency can not beattained. Whereas, in Examples 1 to 9 wherein the primary particle sizeof the abrasive is within a range of from 50 to 120 nm, particularly inExamples other than Examples 1 and 5, wherein the primary particle sizeof the abrasive is in a preferred range (70 to 100 nm), it is evidentthat in each case, a normal polished surface having no pits or scratchescan be obtained, and polishing with high efficiency can be attained.

EXAMPLES 10 to 27 and COMPARATIVE EXAMPLES 7 to 14

[0079] Contents and Preparation of Polishing Compositions

[0080] Colloidal silica having a primary particle size of 90 nm, as anabrasive, glycine, as a compound to form a chelate with copper ions,BTA, as a compound to provide a protective layer-forming function to acopper layer, and hydrogen peroxide, were mixed with water so that theywere blended in such ratios as identified in Table 2, to obtainpolishing compositions of Examples 10 to 27 and Comparative Examples 7to 14. Here, in Comparative Example 7 or 8, the content of the abrasiveis outside the range of from 5 to 50 g/l, based on the composition, inComparative Example 9 or 10, the content of glycine (a compound to forma chelate with copper ions) is outside the range of from 0.04 to 0.2mol/l, based on the composition, in Comparative Example 11 or 12, thecontent of benzotriazole (a compound to provide a protectivelayer-forming function to a copper layer) is outside the range of from0.0002 to 0.002 mol/l, based on the composition, and in ComparativeExample 13 or 14, the content of hydrogen peroxide is outside the rangeof from 0.03 to 1 mol/l, based on the composition. Further, as hydrogenperoxide, a commercially available 31% aqueous solution was employed,and it was mixed immediately before polishing. TABLE 2 Stock Stockremoval removal Benzo- Hydrogen rate of rate of Abrasive Glycinetriazole peroxide copper tantalum (g/l) (mol/l) (mol/l) (mol/l) (Å/min)(Å/min) Ex. 10 5 0.09 0.0005 0.3 2405 7 Ex. 11 10 0.09 0.0005 0.3 3774 8Ex. 12 15 0.09 0.0005 0.3 4194 8 Ex. 13 25 0.09 0.0005 0.3 5082 10 Ex.14 30 0.09 0.0005 0.3 5546 10 Ex. 15 50 0.09 0.0005 0.3 6485 50 Ex. 1620 0.04 0.0005 0.3 4331 11 Ex. 17 20 0.06 0.0005 0.3 5457 11 Ex. 18 200.12 0.0005 0.3 7432 10 Ex. 19 20 0.2 0.0005 0.3 9012 10 Ex. 20 20 0.090.0002 0.3 6457 10 Ex. 21 20 0.09 0.0003 0.3 5909 11 Ex. 22 20 0.090.001 0.3 2445 10 Ex. 23 20 0.09 0.002 0.3 2188 11 Ex. 24 20 0.09 0.00050.03 5495 11 Ex. 25 20 0.09 0.0005 0.1 8141 11 Ex. 26 20 0.09 0.0005 0.35407 11 Ex. 27 20 0.09 0.0005 0.5 5069 10 Comp. 3 0.09 0.0005 1.0 2150 6Ex. 7 Comp. 7 0.09 0.0005 0.3 7559 81 Ex. 8 Comp. Ex. 9 20 0.02 0.00050.3 2415 10 Comp. Ex. 10 20 0.3 0.0005 0.3 12067 9 Comp. Ex. 11 20 0.090.0001 0.3 6954 10 Comp. Ex. 12 20 0.09 0.003 0.3 1402 10 Coinp. Ex. 1320 0.09 0.0005 0.02 2803 10 Comp. 20 0.09 0.0005 2.0 3911 10 Ex. 14

[0081] Polishing Tests

[0082] Using each of the polishing compositions of Examples 10 to 35,polishing of the layer-formed side of an object to be polished, wascarried out under the following conditions:

[0083] Object to be polished:

[0084] A silicon wafer having a copper layer formed by sputtering, and asilicon wafer having a tantalum layer formed by sputtering

[0085] Polishing machine:

[0086] One side CMP polishing machine (AVANTI472, manufactured bySpeedfam-Ipec Co.)

[0087] Polishing pad:

[0088] Laminated polishing pad made of polyurethane (IC-1000/Suba400,manufactured by Rodel Inc., U.S.A.)

[0089] Polishing pressure: 4 psi (about 27.5 kPa)

[0090] Plate rotational speed: 50 rpm

[0091] Feed rate of the polishing composition: 250 cc/min

[0092] Carrier rotational speed: 50 rpm

[0093] Polishing time:

[0094] The copper layer-formed wafer was mounted and polished for oneminute, and then it was changed to the tantalum layer-formed wafer,which was likewise polished for one minute.

[0095] After the polishing, the wafers were sequentially washed anddried, and the layer thicknesses were measured by a sheet resistancedetecting method, and the stock removal rates were obtained from thedifferences in the layer thicknesses as between before and after thepolishing. The obtained results are shown in Table 2.

[0096] As is evident from Table 2, if the content of the abrasive issmaller than the above range, as in Comparative Example 7, the stockremoval rate of the copper layer tends to be low, and polishingtreatment can not be carried out in a short time, whereby it tends to bedifficult to increase the productivity. Further, if the content of theabrasive is larger than the above range as in Comparative Example 8, thestock removal rate of not only the copper layer but also thetantalum-containing compound layer tends to be high, whereby it will bedifficult to control the polishing of the tantalum-containing compoundlayer.

[0097] Further, if the content of glycine is smaller than the aboverange as in Comparative Example 9, the stock removal rate of the copperlayer tends to be low as in Comparative Example 7, and if it exceeds theabove range as in Comparative Example 10, the stock removal rate of thecopper layer tends to be too large, and it tends to be difficult tocontrol the polishing.

[0098] Further, if the content of benzotriazole is smaller than theabove range as in Comparative Example 11, the stock removal rate of thecopper layer tends to be high, but the polished surface after thepolishing tends to be corroded, whereby the smoothness tends to be poor,i.e. the surface is chemically polished more than necessary, wherebyimprovement of the quality can not be attained, although this is notshown in Table 2. Further, if the content of benzotriazole is largerthan the above range as in Comparative Example 12, the etching action tothe copper layer tends to be controlled too much, and the stock removalrate tends to be low.

[0099] Further, if the content of hydrogen peroxide is smaller or largerthan the above range as in Comparative Example 13 or 14, the stockremoval rate of the copper layer tends to be small, and the polishingtreatment can hardly be carried out in a short time, whereby it tends tobe difficult to increase the productivity.

[0100] Whereas, in Examples 10 to 27 wherein the abrasive, glycine,benzotriazole and hydrogen peroxide are within the above ranges, in eachcase, the stock removal rate of the copper layer is high, and the stockremoval rate of the tantalum-containing compound layer is low. Namely,Examples 10 to 27 present polishing compositions which provide highselectivity ratios, whereby polishing excellent in the smoothness of thepolished surface after the polishing can be attained.

[0101] Further, by using each of the polishing compositions of Examples10 to 27, a patterned wafer having a copper wiring with a minimum wirewidth of 0.2 μm formed by electroplating, was polished, whereby no pitsor scratches were observed on the copper layer surface in each case.Thus, it is evident that each of the polishing compositions of Examples10 to 27 is capable of preventing formation of pits in the copperwiring, whereby polishing with high efficiency can be attained.

[0102] As described in the foregoing, the polishing composition of thepresent invention comprises (a) an abrasive, (b) a compound to form achelate with copper ions, (c) a compound to provide a protectivelayer-forming function to a copper layer, (d) hydrogen peroxide and (e)water, wherein the abrasive of component (a) has a primary particle sizewithin a range of from 50 to 120 nm.

[0103] It is thereby possible to obtain a polishing composition which iscapable of preventing formation of pits in a copper wiring in a CMPprocess of a semiconductor device comprising at least a copper layer anda tantalum-containing compound layer.

[0104] In the polishing composition of the present invention, thecontent of the abrasive of component (a) is within a range of from 5 to50 g/l based on the composition, whereby a polishing composition can beobtained which is capable of carrying out mechanical polishing of thecopper layer in a short period of time while suppressing mechanicalpolishing of the tantalum-containing compound layer.

[0105] In the polishing composition of the present invention, thecompound to form a chelate with copper ions, of component (b), is atleast one member selected from the group consisting of glycine,α-alanine, serine, quinaldic acid, hystidine and derivatives thereof,and its content is within a range of from 0.04 to 0.2 mol/l, based onthe composition, whereby it is possible to obtain a polishingcomposition which is capable of carrying out proper polishing of thecopper layer.

[0106] In the polishing composition of the present invention, thecompound to provide a protective layer-forming function to a copperlayer, of component (c), is at least one member selected from the groupconsisting of benzotriazole and its derivatives, and its content iswithin a range of from 0.0002 to 0.002 mol/l, based on the composition,whereby it is possible to obtain a polishing composition which providesthe optimum polishing function by accelerating polishing of the copperlayer and at the same time providing a protective layer-formingfunction.

[0107] In the polishing composition of the present invention, thecontent of hydrogen peroxide of component (d) is within a range of from0.03 to 1 mol/l based on the composition, whereby a polishingcomposition can be obtained which is capable of polishing in a shorttime and which is capable of providing an optimum chemical polishing ofa copper layer.

[0108] The polishing method of the present invention is a method forpolishing a semiconductor device having at least a layer made of copperand a layer made of a tantalum-containing compound, on a substrate, withthe above-mentioned polishing composition, whereby in its CMP process,the stock removal rate of the copper layer will be high, the stockremoval rate of the tantalum-containing compound layer is low, whereby ahigh selectivity ratio can be provided, and a polished surface excellentin smoothness can be obtained, and at the same time, by strictlyspecifying the primary particle size of the abrasive, it is possible toproduce a semiconductor device with a normal polished surface withoutformation of pits on the copper wiring on the substrate.

What is claimed is:
 1. A polishing composition comprising: (a) anabrasive, (b) a compound to form a chelate with copper ions (c) acompound to provide a protective layer-forming function to a copperlayer, (d) hydrogen peroxide, and (e) water, wherein the abrasive ofcomponent (a) has a primary particle size within a range of from 50 to120 nm.
 2. The polishing composition according to claim 1, wherein theabrasive of component (a) is silicon dioxide.
 3. The polishingcomposition according to claim 1, wherein the abrasive of component (a)is fumed silica or colloidal silica.
 4. The polishing compositionaccording to claim 1, wherein the content of the abrasive of component(a) is within a range of from 5 to 50 g/l based on the composition. 5.The polishing composition according to claim 1, wherein the compound toform a chelate with copper ions of component (b), is at least one memberselected from the group consisting of glycine, α-alanine, serine,quinaldic acid, hystidine and derivatives thereof, and its content iswithin a range of from 5 to 50 g/l based on the composition.
 6. Thepolishing composition according to claim 1, wherein the compound toprovide a protective-layer forming function to a copper layer, ofcomponent (c), is at least one member selected from the group consistingof benzotriazole and derivatives thereof, and its content is within arange of 0.0002 to 0.002 mol/l based on the composition.
 7. Thepolishing composition according to claim 1, wherein the content of thehydrogen peroxide of component (d) is within a range of from 0.03 to 1mol/l based on the composition.
 8. A polishing method which comprisespolishing a semiconductor device having at least a layer of copper and alayer of a tantalum-containing compound formed on a substrate, with thepolishing composition as defined in claim 1.